It is previously known to use sun sensors comprising a photochromic ink to measure the UV intensity. For instance, US2005285050 discloses a container for sunscreen agent comprising a sun detector designed to indicate when the cumulative UV radiation to which the bottle (detector) has been exposed reaches a threshold value. Further, sun detectors of a similar nature have previously been used on “sun cards” and on bracelets for the user/wearer to determine the strength of solar radiation.
There is a widespread and ever-increasing need for protection against UV radiation due to the risk of cancer, while many people still desire to spend time in the sun because it is pleasant or in order to tan (i.e., for beauty reasons). Being able to tan safely is therefore desirable, and there is a need for new and improved products for the purpose.